Phosphate framework material possesses fairly well thermal stability and high voltage capabilities required for applications as electrodes e.g. anode or cathode in rechargeable sodium ion batteries. The major drawbacks which hinder the successful application of such type of material in commercial scale, however, lie in the poor electronic and ionic conductivity in its bulk form. Before such drawbacks are successfully overcome, this type of material may not be considered to be suitable for use in rechargeable sodium ion batteries. Attempts have been made to downsizing of the material to enhance the sodium intercalation/de-intercalation properties. However, downsizing will reduce the diffusion length for Na+−ions but may not effectively enhance the electron transportation to the current collector since particle-to-particle boundaries also increased with the downsizing, which can cause electron transportation to be sluggish. As a consequence, electronic conductivity may remain poor and the overall sodium-ion storage is limited.
It is therefore desirable to provide an electrode material having the necessary thermal stabilities and high voltage capacity as well as the electronic/ionic conductivities at a level acceptable for rechargeable sodium ion battery applications. Such a solution is currently not available.